Abstract: An electrophotographic reproduction machine including an image bearing member, latent image devices for forming on the image bearing member electrostatic latent images having a first relative polarity, and a hybrid development unit for applying to the latent images correct-sign toner particles having a second polarity relatively opposite to the first polarity. A detecting apparatus adjacent the image bearing member for sensing toner particles developed into non-image regions. The development unit includes a first biasing means including a DC power supply for biasing a magnetic roll mounted within the housing of the hybrid development unit. A second biasing means includes a second DC power for biasing a donor roll mounted which forms a toner transfer nip with the magnetic roll. The DC power supplies is adjusted so that "wrong sign" toner of said first polarity are attracted to the donor roll from the magnetic brush within the housing of the hybrid development unit.